POUGHKEEPSKIE, N.Y. – A hard parachute opening fractured the spine of a skydiving instructor, causing him to become incapacitated and leading to the fatal tandem jump in Ulster County on June 15, Dutchess County Medical Examiner Dr. Kari Reiber revealed Friday.

The accident killed 25-year-old Alexander Chulsky, an instructor at Skydive the Ranch, and Chappaqua real estate executive David Winoker, 49. Winoker was the president of Manhattan-based Winoker Realty.

"The hard opening of the chute caused a fracture of his upper spine, and this fracture caused an aortic injury, and this was an injury that was completely incapacitating," Reiber said. "That’s why he was not able to control the parachute."

The autopsy could not determine whether Chulsky was killed by the mid-air injury or the fall, but Reibler said the injury was fatal.